#include<bits/stdc++.h>
#define ll long long
#define deb(x) cerr<<"deb:"<<__LINE__<<" "<<#x<<"="<<x<<"\n"
//#define getchar()(p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)
using namespace std;
//char buf[1<<21],*p1=buf,*p2=buf;
inline ll read()
{
	ll sum=0,l=1;char c=getchar();
	while(!isdigit(c)){if(c=='-')l=-1;c=getchar();}
	while(isdigit(c)){sum=(sum<<1)+(sum<<3)+(c^48);c=getchar();}
	return sum*l;
}
ll head[200100],cnt,ans,l,ed,fa[200100],vis[200100],ds[200100],s[200100],tot;
vector<ll> v[200100];
struct edge
{
	ll v,next;
}a[400100];
void Add(ll u,ll v)
{
	a[++cnt].v=v;
	a[cnt].next=head[u];
	head[u]=cnt;
}
void dfs(ll x,ll f,ll dis)
{
	fa[x]=f;
	ds[x]=dis;
	if(x==ed)l=dis;
	ans=max(ans,dis);
	for(ll i=head[x];i;i=a[i].next)
	{
		if(a[i].v==f)continue;
		dfs(a[i].v,x,dis+1);
	}
}
void dfs2(ll x,ll f)
{
	fa[x]=f;
	for(ll i=head[x];i;i=a[i].next)
	{
		if(a[i].v==f||vis[a[i].v])continue;
		dfs2(a[i].v,x);
	}
}
int main()
{
	ll t=read();
	while(t--)
	{
		ll b=read(),c=read(),d=read();
		cnt=0;
		for(ll i=0;i<=b;i++)head[i]=0,vis[i]=0;
		for(ll i=1;i<b;i++)
		{
			ll e=read(),f=read();
			Add(e,f);
			Add(f,e);
		}
		ans=0;
		ed=d;
		dfs(c,0,0);
		ll res=(b-1)*2-ans;
		ed=0;
		ll now=d;
		tot=0;
		while(now)
		{
			vis[now]=1;
			s[++tot]=now;
			if(now==c)break;
			now=fa[now];
		}
		for(ll i=1;i<=tot;i++)
		{
			dfs2(s[i],0);
		}
		dfs(d,0,0);
		for(ll i=1;i<=b;i++)
		{
			v[ds[i]].push_back(i);
		}
		for(ll i=b;i>=0;i--)
		{
			if(v[i].size())
			{
				res=min(res,l+i);
				for(auto p:v[i])
				{
					now=p;
					while(!vis[now])
					{
						vis[now]=1;
						l+=2;
						now=fa[now];
					}
				}
				v[i].clear();
			}
		}
		cout<<res<<"\n";
	}
	return 0;
}